1. Field of the Invention
The present invention relates to a wireless communication device that performs communication by wireless.
Priority is claimed on Japanese Patent Application No. 2005-150183, filed May 23, 2005, the content of which is incorporated herein by reference.
2. Description of Related Art
With the increasing functionality of wireless communication devices that use wireless communication networks such as mobile telephones and in-car communication devices, there are some capable of communication by a plurality of communication systems. Using mobile telephones as an example, some are capable of wireless communication using wireless LAN in addition to a wireless communication system for mobile communication. Mobile telephones have a characteristic in which the radius of the service area of a single access point (base station) is around 2 kilometers. Note that with regard to communication speed, the maximum downlink (from the base station to the wireless communication device) speeds of 2.4 Mbps have become attainable.
On the other hand, among wireless LAN systems that perform network connection within a comparatively restricted area by wireless communication via electromagnetic waves or optical signals without using cables, for example, the IEEE802.11b standard enables a maximum communication speed of 11 Mbps, which is faster than the above-mentioned conventional communication system. However, this standard is characterized by the radius of the area of a single access point being 50 to 100 m, which is narrower than the above-mentioned conventional communication system.
Incidentally, in wireless LAN systems, a mobile IP technology has been proposed in which many access points are set up similarly to mobile telephones, and so even if the access point changes, continuous access is possible. In this mobile IP technology, the network is split into a network to which a mobile terminal (mobile node: MN) originally belongs and an external network, with a home agent (HA), which is a router, provided in the network to which the MN originally belongs, and a foreign agent (FA), which is a router, provided in the destination network of the MN. Also, a home address (HoA), which is a fixed IP address that does not rely on an access point, is assigned to the MN, with the HA managing the relationship between the HoA and a Care-of Address (CoA) using the CoA in the visited network.
Here, assuming the MN has moved from the network to which the MN originally belongs, it automatically acquires a CoA in the destination network, and in order to perform correlation between the CoA and the HoA, the MN sends a registration request to the HA via the FA. The HA, upon receiving this registration request, sends an agent advertisement (data containing an IP address and the like) to the MN. When the MN receives this, the position registration of the MN is completed.
Since a correspondent node (CN) appears to be positioned in the network in which the MN originally belongs, it sends data to be sent to the MN to the HA. The HA then encapsulates packets sent to the MN and sends them to the CoA. The FA receives these encapsulated packets, and forwards them to the IP address of the MN. Thereby, continuous access is possible even if the access point changes. Note that, for details of mobile IP technology, Patent Document 1 (Japanese Unexamined Patent Application, First Publication No. 2001-224070) given below should be referred to.
Incidentally, a wireless communication device such as a mobile telephone is based on a dialup connection. The aforedescribed mobile IP technology is technology designed on the premise of movement between communication mediums such as Ethernet (™). Therefore, it is not optimized for a communication system that is based on dialup connections. Also, since the IP packets in the registration request to the HA described above are discarded, there is a possibility of the session being cut off. Further, depending on the communication condition (high error rate, etc), the registration request may take time, leading to the possibility of the session being cut off.
Also, in mobile communication that is generally employed as described above (wide-area wireless communication network), when moving (changing) between different wide-area wireless communication networks, it is necessary to disconnect the dialup connection that is already established, perform dialup in the new wide-area wireless communication network, and reconnect. For example, an information processing device (personal computer or the like) to which is connected a data communication card for a plurality of different wide communication networks performs communication by seamlessly switching between wireless communication networks.
On the other hand, even in the case of movement (change) of different coverage areas within the same wide-area wireless communication network, during movement so as to straddle devices that manage the IP address given to a wireless communication device, similarly to the case of moving between different wide-area wireless communication networks, it is necessary to disconnect the dial-up connection that is already established, perform dialup in the new area, and reconnect.
As above, in the case of movement that straddles the boundaries of the same or different wide-area wireless communication networks, it is necessary to disconnect the dialup connection and establish a new dialup connection. Also, since anywhere from 10 odd to 20 odd seconds are required from disconnecting the dialup connection to completion of the reconnection, there is the problem that communication cannot be performed during this time.
The present invention was achieved in view of the above circumstances, and has as its object to provide a wireless communication device that can continuously perform communication even in the case of movement that crosses the boundary of the same or different types of wide-area wireless communication networks.